We consider graphs \(G\)  that are simple both in a graph theoretic
and in a topological sense. Thus there are no multi-edges or loops,
adjacent edges do not cross, and two edges cross at most once in a
drawing. Graphs are often defined by particular properties of a
drawing. The planar graphs, in which edge crossings are excluded,
are the most prominent example. There has been recent interest in
the study of beyond-planar graphs
[1]}, [2]}, [3]}, which are
generally defined by drawings with specific restrictions on
crossings.
